1. Field of the Invention
The present invention relates to the field of apparatus and instruments with self-contained energy sources, more particularly portable electric tools with self-contained power, and has for its object an assembly of tool of the mentioned type with a polymer or lithium ion battery.
2.Description of the Related Art
In what follows, there will be meant by “tool” generally an apparatus or instrument adapted to facilitate the physical action of an operator in the execution of a material task or in executing said task under the control of the operator. By tool assembly, is meant a tool with its self-contained energy source and the supply means for this latter.
There can be cited as tools already made by applicant: electronic pruning shears for the size of fruit trees and grape vines, vegetable bundlers and tools for gathering fruit.
There can also be cited in a non-limitative way, as tools of the mentioned type and produced according to similar technologies: chainsaws, portable lawnmowers with wires, hedge trimmers, jackhammers.
These portable electric power tools are distinguished essentially from comparable tools actuated by sources of hydraulic, pneumatic or electric energy, by the fact that they are self-contained and independent of any external energy source, which permits the operator to be entirely free in his movements. There are also distinguished from self-contained electric portable tools actuated by heat engines, by the absence of pollution, bad odors, vibrations and noise during their operation and by their reliability in use.
It has been demonstrated on the other part that the use of these tools gives rise to comfort of without precedent, because of their silence and their flexibility.
Such portable self-contained electric power tools generally comprise at least three separate functional subassemblies, namely, a first subassembly forming an electrical actuator and generating the mechanical action of the tool, a second subassembly forming an electric energy source and comprising essentially a rechargeable electrochemical battery, and a third subassembly forming a charger adapted for the controlled recharging of the battery.
The appearance and development of these tools are principally due to two technical factors:                on the one hand, the arrival on the market of new types of batteries having better capacity/weight ratio,        on the other hand, the development of technologies of electrical motors with very high output.        
The batteries at present used on tools mentioned as examples are of the nickel cadmium type or the nickel metal hydride type. They have an energy capacity of about 30 to 50 Watt hours per kilogram.
Given that an operator has, in accordance particularly with the official recommendations, a capacity of carrying on his back, in a bandolier or belt, 4 kg maximum for continuous working per day, it has been determined that with present techniques, with nickel cadmium and nickel metal hydride, the total capacity of the battery carried by the operator will be comprised between 150 and 200 Watt hours.
This capacity is not sufficient to give self-contained portable electric power tools, the energy necessary to work half a day, nor of course a full day.
There thus exists the need and effective demand for batteries having a better capacitance/weight ratio, so as to permit extending the field of application of portable self-contained electric power tools, given their advantages and qualities set forth above.
The invention seeks, to this end, to use the emerging technology of lithium ion and lithium polymer batteries in the context of portable self-contained electric power tools.
Thus, although these batteries are at present frequently used in mobile phones, camcorders and portable computers, they are not yet used in applications of portable electric tools, particularly power tools, given the difficulties encountered in their use in this application. However, they offer capacitance/weight ratios of 150 to 200 Watt hours per kilogram, which would permit tripling, or even quadrupling, the power or the lifetime of these portable electric tools, relative to their present possibilities with nickel cadmium or nickel metal hydride batteries.
It should be noted that, given the power requirement, the use of lithium ion and lithium polymer batteries in the application to portable electric power tools requires the provision of high voltages.
Thus, lithium ion and lithium polymer elements cannot by their nature deliver a high current and because of this require the coupling of basic elements in series, so as to obtain high voltages, permitting in this way the supply of substantial power despite a weak current.
Thus, for the formation of batteries delivering electrical power suitable for applications in portable self-contained power tools, whilst respecting the laws in force as to usage voltage and by providing useful working voltages, there should be provided series couplings of numerous elements or numerous cells, each of these latter containing several elements in parallel.
There result substantial difficulties for controlling and operating such batteries of multiple components, which have not to this day been solved.
Thus, the in applications previously cited (mobile phones, camcorders and portable computers) the batteries comprise in general at most four elements associated in series, whose use during charging and discharging is less complex and relatively easy to use.